Technical Field
The present disclosure generally relates to machine-readable symbol readers.
Description of the Related Art
Machine-readable symbols encode information in a form that can be optically read via a machine-readable symbol reader or scanner. Machine-readable symbols take a variety of forms, the most commonly recognized form being the linear or one-dimensional machine-readable symbol. Other forms include two-dimensional machine-readable symbols such as stacked code symbols, area or matrix code symbols, or digital watermarks. These machine-readable symbols may be made of patterns of high and low reflectance areas. For instance, a one-dimensional or barcode symbol may comprise a pattern of black bars on a white background. Also for instance, a two-dimensional symbol may comprise a pattern of black marks (e.g., bars, squares or hexagons) on a white background. Machine-readable symbols are not limited to being black and white, but may comprise two other colors or two different reflective property areas, and/or may include more than two colors (e.g., more than black and white). Machine-readable symbols may also include human-readable symbols (e.g., alpha, numeric, punctuation).
Machine-readable symbols are typically composed of elements (e.g., symbol characters) which are selected from a particular machine-readable symbology. Information is encoded in the particular sequence of shapes (e.g., bars, dots) and spaces which may have varying dimensions. The machine-readable symbology provides a mapping between machine-readable symbols or symbol characters and human-readable symbols (e.g., alpha, numeric, punctuation, commands). A large number of symbologies have been developed and are in use, for example Universal Product Code (UPC), International Article Number (EAN), Code 39, Code 128, Data Matrix, PDF417, etc.
Machine-readable symbols have widespread and varied applications. For example, machine-readable symbols can be used to identify a class of objects (e.g., merchandise) or unique objects (e.g., patents). As a result, machine-readable symbols are found on a wide variety of objects, such as retail goods, company assets, and documents, and help track production at manufacturing facilities and inventory at stores (e.g., by scanning objects as they arrive and as they are sold). In addition, machine-readable symbols may appear on a display of a portable electronic device, such as a mobile telephone, personal digital assistant, tablet computer, laptop computer, or other device having an electronic display. For example, a customer, such as a shopper, airline passenger, or person attending a sporting event or theater event, may cause a machine-readable symbol to be displayed on their portable electronic device so that a merchant (e.g., via a merchant-employee) can read the machine-readable symbol via a machine-readable symbol reader to allow the customer to redeem a coupon or to verify that the customer has purchased a ticket for the event.
Machine-readable symbol readers or scanners are used to capture images or representations of machine-readable symbols appearing on various surfaces to read the information encoded in the machine-readable symbol. One commonly used machine-readable symbol reader is an imager- or imaging-based machine-readable symbol reader. Imaging-based machine-readable symbol readers typically employ flood illumination to simultaneously illuminate the entire machine-readable symbol, either from dedicated light sources, or in some instances using ambient light. Such is in contrast to scanning or laser-based (i.e., flying spot) type machine-readable symbol readers, which scan a relative narrow beam or spot of light sequentially across the machine-readable symbol.
Machine-readable symbol readers may be fixed, for example, readers may be commonly found at supermarket checkout stands or other point of sale locations. Machine-readable symbol readers may also be handheld (e.g., handheld readers or even smartphones), or mobile (e.g., mounted on a vehicle such as a lift vehicle or a forklift).
Imaging-based machine-readable symbol readers typically include solid-state image circuitry, such as charge-coupled devices (CCDs) or complementary metal-oxide semiconductor (CMOS) devices, and may be implemented using a one-dimensional or two-dimensional imaging array of photosensors (or pixels) to capture an image of the machine-readable symbol. One-dimensional CCD or CMOS readers capture a linear cross-section of the machine-readable symbol, producing an analog waveform whose amplitude represents the relative darkness and lightness of the machine-readable symbol. Two-dimensional CCD or CMOS readers may capture an entire two-dimensional image. The image is then processed to find and decode a machine-readable symbol. For example, virtual scan line techniques for digitally processing an image containing a machine-readable symbol sample across an image along a plurality of lines, typically spaced apart and at various angles, somewhat like a scan pattern of a laser beam in a scanning or laser-based scanner.
Direct part marking (DPM) is a process for imprinting a machine-readable symbol directly on an item or surface in a permanent manner instead of printing the symbol on a paper label that is adhered or attached to a surface. The intent is to create a permanent identifier for the item. In some applications, 2D machine-readable symbols are used in DPM technology. The use of DPM technology is becoming increasingly popular in many applications as manufacturers are required to trace their products from beginning to end throughout the supply chain. This tracking ability needs to endure regardless of the size of the symbol, the surface material involved, or where a component might be shipped to on a global basis. The main benefit of DPM technology is its durability. The permanent nature of the marking assures that the item can be identified throughout its full life cycle and throughout the supply chain, even while being exposed to harsh environmental conditions.
In many cases, machine-readable symbols marked with DPM technology are used to identify and track unique items such as spare parts or components. Another important benefit of DPM technology is that DPM technology allows the marking of very small codes in limited spaces where a standard label cannot be applied. The high variability of the surface material (metal, plastic, glass, etc.) and the reduced size of the symbols marked with DPM offer unique challenges to the device used to read the machine-readable symbols. For DPM technology to be successful in providing traceability and increased operational efficiency, multiple factors need to be considered before choosing DPM technology as the right solution for lifetime product traceability.
DPM technology may be suitable for various industries. While the use of machine-readable symbols marked with DPM technology were first adopted by the automotive sector, the popularity of DPM technology has spread to aerospace, defense, electronics and computers, healthcare, raw materials, jewelry and more. Machine-readable symbols marked with DPM can be implemented on different surfaces and materials including plastic, metal, wood, rubber, leather, glass, etc. The use of 2D symbols provides the capacity to encode a large amount of data in a very limited space. Indeed, manufacturers use DPM technology to enhance the supply chain traceability of car components, medical tools, weapons and defense equipment, fine jewelry, electronic parts or any application where there is the need to experience harsh chemical treatment, endure extreme conditions of moisture or temperature, include high-value assets or items that need to be identified throughout their lifetime.
There are multiple methods for directly marking objects, including laser etching, chemical etching, dot peening, and ink jet printing, for example. Each of these methods has specific advantages and disadvantages in terms of durability, cost and ease of reading.
Laser etching may be the most widely used method because it is applicable to many different materials while offering good marking qualities. This technique does not involve the use of inks, nor does it involve tool bits which contact the engraving surface. However, laser etching affects the material being marked, creating a change of the material characteristics through the interaction with a laser beam. By turning the laser on and off, the laser beam draws or etches the machine-readable symbol on the surface of the material. Depending on the laser strength, the surface changes are affected by ablation, engraving, color change, annealing or surface oxidation.
Chemical etching includes masking to limit the affected area. In some situations, chemical etching may be achieved via multiple manufacturing processes to apply the mask, etch the symbol, and remove the mask.
Dot peening, also known as point of percussion technology, includes a series of mechanical percussions done by a machine and a needle called “peen.” Impressions or recesses are made at specific locations modifying the depth of the surface which creates differences in the light reflection and diffusion which is needed to identify light and dark elements of the symbol. This technology is generally considered the most durable solution.
FIG. 1 shows a schematic representation of the various shapes of recesses obtainable by dot peening. In a top row of FIG. 1, three marking pins 10, 12 and 14 for a dot peen system are shown. The middle row of FIG. 1 provides a schematic top plan view of recesses 22, 24 and 26 generated by the marking pins 10, 12 and 14, respectively. The bottom row of FIG. 1 shows a schematic sectional view of the recesses 22, 24 and 26.
The marking pins 10, 12 and 14 include respective cone-shaped tips 16, 18 and 20 which have opening angles of 60 degrees, 90 degrees, and 120 degrees, respectively. As shown in the middle row of FIG. 1, the marking pin 10 generates the recess 22 which has a diameter D1 and a marking depth or height H1, the marking pin 12 generates the recess 24 which has a diameter D2 and a height H2, and the marking pin 14 generates the recess 26 which has a diameter D3 and a height H3. As shown, D1 is less than D2, which is less than D3. Further, H1 is greater than H2, which is greater than H3. Thus, by selecting the particular shape of the marking pin, the diameter and marking depth may be adjusted to be suitable for a particular application.
As shown in the bottom row of FIG. 1, the tip 16 of the marking pin 10 generates the recess 22 and a raised ring or rim 34 surrounding a valley 40. Similarly, the tip 18 of the marking pin 12 generates the recess 24 and a raised ring or rim 36 surrounding a valley 42, and the tip 20 of the marking pin 14 generates the recess 26 and a raised ring or rim 38 surrounding a valley 44.
Ink jet printing includes projecting ink onto the surface of the items, and producing a pattern of spots constituting the symbol by ink deposit. While this process is not suitable for harsh environments, the advantage of this technology is that it can be used on all types of surfaces and eliminates the need for a paper label.
Yet, the use of imaging readers, especially handheld readers, for reading DPM codes on workpieces has proven to be challenging. Contrast is still often less than desirable. Ambient lighting conditions are variable. Illumination from on-board illuminators or illumination light sources is directed at variable angles. Reflections from ambient light sources and illumination light sources often appear in the field of view of the reader as hot spots, glare, or specular reflections of intense, bright light that saturate the imagers, thereby degrading reading performance.
In addition, aiming the handheld imaging readers at the DPM codes, prior to reading the DPM codes, has proven to be difficult. Requiring an operator to aim the reader at the DPM codes makes the process of locating and decoding the DPM codes faster and easier. Unlike machine-readable codes printed in one color (for example, black) on paper of another color (for example, white), DPM codes are typically difficult for a human operator to even find on the workpieces, which often have complicated, e.g., non-planar, curved, reflective surfaces, to further complicate finding the DPM codes and aiming the reader directly at the DPM codes for reading.